The Rig Veda describes soma's habitat, preparation and effects, but the living tradition lost the plant before the late Vedic period, when the ritual texts already prescribe substitutes. Two centuries of proposals (ephedra, fly agaric, Syrian rue, and others, including Wasson's 1968 book-length fly agaric case) each fit some verses and fail others, and no candidate has won consensus.
What would resolve this Archaeobotanical residue analysis from an early Vedic or BMAC-context ritual vessel with identifiable plant remains, or a decisive phytochemical match between the full Rigvedic description and a candidate species in its Indo-Iranian range.
OpenArchaeobotany and Vedic philologyStephanie W. Jamison and Joel P. Brereton, The Rigveda: The Earliest Religious Poetry of India